The overall goal of this project is to understand how neuronal responses to sensory stimuli are coordinated in the cerebral cortex, both locally and across connnected cortical areas. Somatosensory information is important for guiding many motor behaviors, and this is mediated by projections from somatosensory cortex to brain regions involved in controlling motor output. Hence, increased knowledge of these pathways and the mechanisms that govern long-range interactions between the primary somatosensory (SI) cortex and the primary motor (Ml) cortex should facilitate the development of new strategies and techniques for rehabilitating brain-damaged individuals that suffer sensory impairment: We will use the rodent SI barrel cortex as an animal model to test several hypotheses concerning the corticocortical projections from SI to MI. For Specific Aim 1, the distribution of retrogradely-labled neurons in the barrel field of SI will be characterized following discrete deposits of two tracers into neighboring focal sites of MI. By using a dual tracing paradigm, we will determine the topography of SI neurons that converge on focal sites in MI cortex. For Specific Aim 2, we will simultaneously record multiple neurons in SI barrel cortex to characterize how different types of neurons are coordinated with each other during sensory stimulation. Thus, we will characterize the coordination or relative timing of discharges among: a) pairs of SI neurons that project to MI, b) pairs of SI neurons that do not project to Ml, and c) heterogeneous pairs of projection and non-projection neurons. For Specific Aim 3 we will simultaneously record multiple neurons in connected parts of SI and MI to test the hypothesis that neighboring pairs of projection neurons in SI cooperate with each other to activate common neuronal targets in MI cortex. To address this issue, conditional cross-correlation analysis will be used to quantify the impact of synchronized activity in SI on the probability of neuronal responsiveness in corresponding parts of the MI whisker representation.